diff options
author | Russ Cox <rsc@golang.org> | 2014-06-11 14:21:06 -0400 |
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committer | Russ Cox <rsc@golang.org> | 2014-06-11 14:21:06 -0400 |
commit | 80a3f744d6f93f4d120fab06af963dab8ce9d8e0 (patch) | |
tree | b72d19956386aa4ede98a4fa49949ddf200c2343 | |
parent | c80394890fc23e1bb14e69be7c34623984772f73 (diff) | |
download | go-80a3f744d6f93f4d120fab06af963dab8ce9d8e0.tar.gz |
cmd/gc: fix &result escaping into result
There is a hierarchy of location defined by loop depth:
-1 = the heap
0 = function results
1 = local variables (and parameters)
2 = local variable declared inside a loop
3 = local variable declared inside a loop inside a loop
etc
In general if an address from loopdepth n is assigned to
something in loop depth m < n, that indicates an extended
lifetime of some form that requires a heap allocation.
Function results can be local variables too, though, and so
they don't actually fit into the hierarchy very well.
Treat the address of a function result as level 1 so that
if it is written back into a result, the address is treated
as escaping.
Fixes issue 8185.
LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/108870044
-rw-r--r-- | src/cmd/gc/esc.c | 13 | ||||
-rw-r--r-- | test/escape2.go | 12 |
2 files changed, 23 insertions, 2 deletions
diff --git a/src/cmd/gc/esc.c b/src/cmd/gc/esc.c index 9d7dc1149..78624d7cb 100644 --- a/src/cmd/gc/esc.c +++ b/src/cmd/gc/esc.c @@ -673,12 +673,21 @@ esc(EscState *e, Node *n, Node *up) // for &x, use loop depth of x if known. // it should always be known, but if not, be conservative // and keep the current loop depth. - if(n->left->op == ONAME && (n->left->escloopdepth != 0 || n->left->class == PPARAMOUT)) { + if(n->left->op == ONAME) { switch(n->left->class) { case PAUTO: + if(n->left->escloopdepth != 0) + n->escloopdepth = n->left->escloopdepth; + break; case PPARAM: case PPARAMOUT: - n->escloopdepth = n->left->escloopdepth; + // PPARAM is loop depth 1 always. + // PPARAMOUT is loop depth 0 for writes + // but considered loop depth 1 for address-of, + // so that writing the address of one result + // to another (or the same) result makes the + // first result move to the heap. + n->escloopdepth = 1; break; } } diff --git a/test/escape2.go b/test/escape2.go index f00741dc2..28251aa98 100644 --- a/test/escape2.go +++ b/test/escape2.go @@ -1478,3 +1478,15 @@ func foo153(v interface{}) *int { // ERROR "leaking param: v" } panic(0) } + +// issue 8185 - &result escaping into result + +func f() (x int, y *int) { // ERROR "moved to heap: x" + y = &x // ERROR "&x escapes to heap" + return +} + +func g() (x interface{}) { // ERROR "moved to heap: x" + x = &x // ERROR "&x escapes to heap" + return +} |